NAME

Xnest - a nested X server

SYNOPSIS

Xnest [-options]

DESCRIPTION

Xnest is a client and a server. Xnest is a client of the
real server which manages windows and graphics requests on
its behalf. Xnest is a server to its own clients. Xnest
manages windows and graphics requests on their behalf. To
these clients Xnest appears to be a conventional server.

OPTIONS

Xnest supports all standard options of the sample server
implementation. For more details, please see the manual
page on your system for Xserver. The following additional
arguments are supported as well.
-displaystring
This option specifies the display name of the real
server that Xnest should try to connect with. If it is
not provided on the command line Xnest will read the
DISPLAY environment variable in order to find out the
same information.
-sync
This option tells Xnest to synchronize its window and
graphics operations with the real server. This is a
useful option for debugging, but it will slow down the
performance considerably. It should not be used unless
absolutely necessary.
-full
This option tells Xnest to utilize full regeneration of
real server objects and reopen a new connection to the
real server each time the nested server regenerates.
The sample server implementation regenerates all objects
in the server when the last client of this server ter-
minates. When this happens, Xnest by default maintains
the same top level window and the same real server con-
nection in each new generation. If the user selects
full regeneration, even the top level window and the
connection to the real server will be regenerated for
each server generation.
-classstring
This option specifies the default visual class of the
nested server. It is similar to the -cc option from the
set of standard options except that it will accept a
string rather than a number for the visual class specif-
ication. The string must be one of the following six
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values: StaticGray, GrayScale, StaticColor, PseudoColor,
TrueColor, or DirectColor. If both, -class and -cc
options are specified, the last instance of either
option assumes precedence. The class of the default
visual of the nested server need not be the same as the
class of the default visual of the real server;
although, it has to be supported by the real server.
See xdpyinfo for a list of supported visual classes on
the real server before starting Xnest. If the user
chooses a static class, all the colors in the default
colormap will be preallocated. If the user chooses a
dynamic class, colors in the default colormap will be
available to individual clients for allocation.
-depthint
This option specifies the default visual depth of the
nested server. The depth of the default visual of the
nested server need not be the same as the depth of the
default visual of the real server; although, it has to
be supported by the real server. See xdpyinfo for a
list of supported visual depths on the real server
before starting Xnest.
-sss
This option tells Xnest to use the software screen
saver. By default Xnest will use the screen saver that
corresponds to the hardware screen saver in the real
server. Of course, even this screen saver is software
generated since Xnest does not control any actual
hardware. However, it is treated as a hardware screen
saver within the sample server code.
-geometryWxH+X+Y
This option specifies geometry parameters for the top
level Xnest windows. These windows corresponds to the
root windows of the nested server. The width and height
specified with this option will be the maximum width and
height of each top level Xnest window. Xnest will allow
the user to make any top level window smaller, but it
will not actually change the size of the nested server
root window. As of yet, there is no mechanism within
the sample server implementation to change the size of
the root window after screen initialization. In order
to do so, one would probably need to extend the X proto-
col. Therefore, it is not likely that this will be
available any time soon. If this option is not speci-
fied Xnest will choose width and height to be 3/4 of the
dimensions of the root window of the real server.
-bwint
This option specifies the border width of the top level
Xnest window. The integer parameter must be a positive
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number. The default border width is 1.
-namestring
This option specifies the name of the top level Xnest
window. The default value is the program name.
-scrnsint
This option specifies the number of screens to create in
the nested server. For each screen, Xnest will create a
separate top level window. Each screen is referenced by
the number after the dot in the client display name
specification. For example, xterm -display :1.1 will
open an xterm client in the nested server with the
display number :1 on the second screen. The number of
screens is limited by the hard coded constant in the
server sample code which is usually 3.
-install
This option tells Xnest to do its own colormap installa-
tion by bypassing the real window manager. For it to
work properly the user will probably have to temporarily
quit the real window manager. By default Xnest will
keep the nested client window whose colormap should be
installed in the real server in the WM_COLORMAP_WINDOWS
property of the top level Xnest window. If this color-
map is of the same visual type as the root window of the
nested server, Xnest will associate this colormap with
the top level Xnest window as well. Since this does not
have to be the case, window managers should look pri-
marily at the WM_COLORMAP_WINDOWS property rather than
the colormap associated with the top level Xnest window.
Unfortunately, window managers are not very good at
doing that yet so this option might come in handy.
-parentwindow_id
This option tells Xnest to use the window_id as the root
window instead of creating a window. This option is used
by the xrx xnestplugin.

USAGE

Starting up Xnest is as simple as starting up xclock from a
terminal emulator. If a user wishes to run Xnest on the
same workstation as the real server, it is important that
the nested server is given its own listening socket address.
Therefore, if there is a server already running on the
user's workstation, Xnest will have to be started up with a
new display number. Since there is usually no more than one
server running on a workstation, specifying Xnest :1 on the
command line will be sufficient for most users. For each
server running on the workstation the display number needs
to be incremented by one. Thus, if you wish to start
another Xnest, you will need to type Xnest :2 on the command
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line.
On some operating environments, you need to add authorisa-
tion cookies to your xauth list before. You might find the
following script useful:
#!/bin/sh
dispnr=${1:-1}
hostname=$(hostname)
COOKIE=$(/usr/sbin/openssl rand -hex 16)
xauth add $hostname/unix:$dispnr . $COOKIE
xauth add localhost/unix:$dispnr . $COOKIE
Xnest :$dispnr
rv=$?
xauth remove $hostname/unix:$dispnr localhost/unix:$dispnr
exit $rv
To run clients in the nested server each client needs to be
given the same display number as the nested server. For
example, xterm -display :1 will start up an xterm in the
first nested server and xterm -display :2 will start an
xterm in the second nested server from the example above.
Additional clients can be started from these xterms in each
nested server.

XNEST AS A CLIENT

Xnest behaves and looks to the real server and other real
clients as another real client. It is a rather demanding
client, however, since almost any window or graphics request
from a nested client will result in a window or graphics
request from Xnest to the real server. Therefore, it is
desirable that Xnest and the real server are on a local net-
work, or even better, on the same machine. As of now, Xnest
assumes that the real server supports the shape extension.
There is no way to turn off this assumption dynamically.
Xnest can be compiled without the shape extension built in,
and in that case the real server need not support it. The
dynamic shape extension selection support should be con-
sidered in further development of Xnest.
Since Xnest need not use the same default visual as the the
real server, the top level window of the Xnest client always
has its own colormap. This implies that other windows'
colors will not be displayed properly while the keyboard or
pointer focus is in the Xnest window, unless the real server
has support for more than one installed colormap at any
time. The colormap associated with the top window of the
Xnest client need not be the appropriate colormap that the
nested server wants installed in the real server. In the
case that a nested client attempts to install a colormap of
a different visual from the default visual of the nested
server, Xnest will put the top window of this nested client
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and all other top windows of the nested clients that use the
same colormap into the WM_COLORMAP_WINDOWS property of the
top level Xnest window on the real server. Thus, it is
important that the real window manager that manages the
Xnest top level window looks at the WM_COLORMAP_WINDOWS pro-
perty rather than the colormap associated with the top level
Xnest window. Since most window managers appear to not
implement this convention properly as of yet, Xnest can
optionally do direct installation of colormaps into the real
server bypassing the real window manager. If the user
chooses this option, it is usually necessary to temporarily
disable the real window manager since it will interfere with
the Xnest scheme of colormap installation.
Keyboard and pointer control procedures of the nested server
change the keyboard and pointer control parameters of the
real server. Therefore, after Xnest is started up, it will
change the keyboard and pointer controls of the real server
to its own internal defaults. Perhaps there should be a
command line option to tell Xnest to inherit the keyboard
and pointer control parameters from the real server rather
than imposing its own. This is a future consideration.

XNEST AS A SERVER

Xnest as a server looks exactly like a real server to its
own clients. For the clients there is no way of telling if
they are running on a real or a nested server.
As already mentioned, Xnest is a very user friendly server
when it comes to customization. Xnest will pick up a number
of command line arguments that can configure its default
visual class and depth, number of screens, etc. In the
future, Xnest should read a customization input file to pro-
vide even greater freedom and simplicity in selecting the
desired layout. Unfortunately, there is no support for
backing store and save under as of yet, but this should also
be considered in the future development of Xnest.
The only apparent intricacy from the users' perspective
about using Xnest as a server is the selection of fonts.
Xnest manages fonts by loading them locally and then passing
the font name to the real server and asking it to load that
font remotely. This approach avoids the overload of sending
the glyph bits across the network for every text operation,
although it is really a bug. The proper implementation of
fonts should be moved into the os layer. The consequence of
this approach is that the user will have to worry about two
different font paths - a local one for the nested server and
a remote one for the real server - since Xnest does not pro-
pagate its font path to the real server. The reason for
this is because real and nested servers need not run on the
same file system which makes the two font paths mutually
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incompatible. Thus, if there is a font in the local font
path of the nested server, there is no guarantee that this
font exists in the remote font path of the real server.
Xlsfonts client, if run on the nested server will list fonts
in the local font path and if run on the real server will
list fonts in the remote font path. Before a font can be
successfully opened by the nested server it has to exist in
local and remote font paths. It is the users' responsibil-
ity to make sure that this is the case.

BUGS

Won't run well on servers supporting different visual
depths. Still crashes randomly. Probably has some memory
leaks.